The present invention relates to rotary drill bits for cutting through subterranean formations and, in particular, to nozzles mounted in the drill bit for discharging drilling fluid.
In a typical rotary drilling operation, a rotary drill bit is rotated while being advanced into a soil or rock formation. The soil or rock is cut by cutting elements on the drill bit, and these cuttings are flushed from the borehole by the circulation of drilling fluid toward the top of the borehole. The drilling fluid is delivered to the drill bit downwardly through a passage in the drill stem and is ejected outwardly through nozzles disposed in bores in the cutting face of the drill bit. The ejected drilling fluid is directed outwardly through the nozzles at high speed to aid in cutting, and to flush and cool the cutter elements.
It is desirable that the drilling fluid be distributed over as wide an area as possible to optimize the cleaning and cooling of the cutting elements. This result could be achieved by maximizing the number of nozzles. The number of nozzles which are able to be utilized, however, is limited by a number of factors, such as the fact that the fluid pressure to each nozzle is reduced as the number of nozzles is increased. This shortcoming cannot be avoided by making the nozzle channels smaller, because the channels would then clog too easily. Also, the nozzles occupy surface area which could otherwise be occupied by cutting elements.